The present invention relates to a system for controlling injection of fuel for a two-cycle engine with a direct fuel injection system where only fuel is injected into a combustion chamber, and more particularly to a system for controlling fuel injection pulse width, injection timing and fuel pressure in accordance with operating conditions of the engine.
There are various methods for supplying the fuel to a two-cycle engine. In one method where the fuel is mixed with air to make a combustible mixture and the mixture is supplied to a cylinder of the engine, a part of the fuel escapes from the cylinder through an exhaust port when scavenging the mixture. In order to prevent the fuel from escaping through the exhaust port, a method in which only the air is delivered to the cylinder and the fuel is injected directly into the cylinder by an injector has been proposed.
Such a direct fuel injection system may be of a type where only high pressurized fuel is injected or a type where low pressurized fuel mixed with air is injected. In order to provide stratified charging, it is preferable to inject only the fuel at high pressure, since the fuel can be injected in a short time and the injection timing can be set near the ignition timing, thereby restraining diffusion of the fuel. Moreover, it is necessary to control the high pressure in relation to the fuel injection quantity and the injection timing, in accordance with engine operating conditions.
Japanese Patent Application Laid-Open 58-143136 discloses a fuel injection control system where fuel pressure is decreased in a light engine load range. As a result, a fuel injection pulse width can be maintained at a length whereby stability of a fuel injection is ensured while decreasing the quantity of the fuel.
Japanese Patent Application laid-Open 59-122734 discloses a fuel injection control system where the fuel pressure is controlled in accordance with engine speed and intake pressure, thereby decreasing the dynamic range of the injector compared to an ordinary system.
However, these fuel injection systems are only for a four-cycle engine and hence the fuel is injected at a low pressure unlike the direct fuel injection system for the two-cycle engine. In particular, the fuel pressure is controlled at a pressure higher than the intake pressure by a predetermined value, and the injection timing is relatively roughly set at a timing before or during an induction stroke. On the other hand, the fuel in the direct fuel injection system for the two-cycle engine must be injected at a high pressure, and the injection timing must be determined in dependency on a closing timing of a scavenge port. Thus, the above-described injection systems cannot be used for the two-cycle engines.